A vehicle is equipped with a power supply control device for controlling power supply from a battery to a load (e.g., JP 2017-103683A). The power supply control device disclosed in JP 2017-103683A turns on or off a switch that is provided in a current path from a battery to a load, according to a switching signal that instructs the switch to turn on or off. Power supply to the load is controlled by this switching operation.
When the switch is on, the voltage across the switch is approximately 0 V. When the switch is off, the voltage across the switch is high. If a period when the switching signal instructs the switch to turn on but the voltage across the switch is not less than a prescribed voltage reaches or exceeds a predetermined period, the power supply control device disclosed in JP 2017-103683A decides that the switch is not turned on properly and detects a switch-related failure. If the switching signal instructs the switch to turn off, the period when the voltage across the switch is not less than the prescribed voltage is initialized to zero.
As a known configuration for supplying electric power to a load, a switch may be turned alternately on and off, that is, turned on and off under PWM (pulse width modulation) control. When electric power is supplied to the load in this configuration, the switching signal instructs the switch to turn alternately on and off. For example, this configuration controls the duty ratio of the switching signal, based on the output voltage of the battery, and can thereby apply the voltage to the load at a prescribed average voltage, irrespective of the varying output voltage of the battery.
Suppose that the power supply control device disclosed in JP 2017-103683A is modified to supply electric power to the load by turning on and off the switch alternately and repeatedly. In this modified configuration, as far as the period when the switching signal continuously instructs the switch to turn on is less than the above-mentioned predetermined period, the period when the voltage across the switch is not less than the prescribed voltage will not reach or exceed the predetermined period. Eventually, even when the switch is not turned on properly in response to the switching signal, this power supply control device does not detect a switch-related failure.
An object of the present disclosure, which is made in consideration of such circumstances, is to provide a power supply control device and a power supply control method which can properly detect a switch-related failure.